CRI (colour rendering index) describes colour fidelity relative to a reference illuminant. On most lighting specifications, “CRI” means the general index Ra, calculated from eight standard test colours. A score of 100 indicates no difference for those samples in the calculation.
What the number leaves out
Ra is an average. It can hide poor performance on a particular colour, and the saturated-red test sample R9 is not one of its eight samples. Check whether a specification gives Ra, individual samples or a different average before comparing numbers.
Using CRI on a film set
A high CRI is useful background information, but it cannot guarantee how a particular camera will render skin, fabrics or products. It also says nothing about output, shadow quality or flicker.
Practical example
For a wardrobe test, compare two fixtures at the intended CCT with the same camera, white balance, exposure and grade. Record the actual fabric and a colour chart. If both lights claim CRI 95, that does not require the fabric to look identical under both.
Related terms
TLCI (Television Lighting Consistency Index) · SSI (Spectral Similarity Index) · CCT (Correlated Colour Temperature) · TM-30
References
CIE: general colour rendering index · NIST: colour rendering of light sources